Method of blasting

ABSTRACT

A method of blasting in which rock pile profile associated with a blast field is controlled by precise control of the detonation delay times between and/or within individual blastholes in the blast field, in combination with the control of one or more other blast parameters.

[0001] The present invention relates to a method of blasting using anadjustable, highly precise blasthole initiation system in combinationwith specific aspects of blast design to provide improved blast results,more specifically to control the rockpile (muckpile) profile associatedwith a blast.

[0002] Blasting operations produce rockpiles of material which is thrown(or displaced) by the blast. The characteristics of the rockpile profile(e.g. shape and displacement) produced influences the extent ofexcavation subsequently required, as well as the productivity of thatexcavation. It would be desirable to provide a method of blasting whichallows the rockpile profile associated with a blast to be controlled andoptimised, thereby allowing the efficiency associated with the blastingoperation to be significantly enhanced by improved excavatorproductivity. It would also be desirable to control and tailor theparticular rockpile profile associated with a blast to the mineexcavation system associated with a particular blast site.

[0003] In accordance with the present invention it has now been foundthat these benefits may be achieved by precise control of certainaspects of blast design. More specifically, the present inventionprovides a method of blasting in which rockpile profile associated witha blast field is controlled by precise control of theinitiation/detonation delay times between and/or within individualblastholes in the blast field, in addition to the control of one or moreother important blast parameters, in particular the blasthole geometry,explosive charge and blast initiation location. This approach isfundamentally different from conventional blasting techniques whichneither provide the adjustable delay times and high precision requirednor generally vary the blasthole geometry, explosive charge and/or blastinitiation location over a blast field specifically for the purpose ofcontrolling the rockpile profile. In conventional blasting techniquesmost blasthole characteristics are generally designed to be constantover the entire blast field, or over large sections of the blast field.It has now been found that particular combinations of delay times, usinghighly precise initiation systems, and one or more of blast geometry,explosive charge and blast initiation location, applied as requireddifferentially to various parts of the blast field, enable tailoring ofthe muckpile.

[0004] In accordance with the present invention precise control of blastdelay time means control within a tolerance of less than one millisecondof the required and intended delay time between adjacent blastholesand/or within individual blastholes. This degree of control may beachieved using an electronic initiation system, as opposed toconventionally used non-electronic initiation systems. In one aspect ofthe invention it has been found that electronic initiation systems allowhighly precise control of the delay between and/or within individualblasthole firings over the blast field and, in turn, this providesenhanced flexibility with respect to blast design such that the benefitsof the present invention may be achieved. In addition, these systems areprogrammable and so provide the capability to obtain the required delaytimes, as opposed to conventional systems, which generally have alimited range of fixed delay times.

[0005] Typically, in accordance with the present invention the blastfield is made up of a number of blastholes, and the invention resides incontrolling the characteristics of the blastholes, particularly theblasthole diameter, geometry and explosive charge contained, incombination with precise control of the detonation delay between and/orwithin the blastholes. In the following the invention will beillustrated by reference to this kind of blast field. It has been foundthat precise control of the delay between blasthole firings allows theeffect of other aspects of blast design on rockpile profile to bemanipulated and optimised. Any one or more of the blastholecharacteristics may be employed in combination with precise firing delaycontrol in order to achieve the desired rockpile in a given situation.

[0006] In accordance with the present invention it is possible tocontrol the magnitude of displacement of the rockpile in a particulardirection and in selected zones of the blast to achieve a desiredrockpile profile. Thus, the profile may be flattened or displacedforwards in certain areas or, alternatively, made to heave upwards or beminimally displaced in other areas as required to suit the mineexcavation system. These possibilities are achieved in accordance withthe present invention by designing the blast based on a high level ofprecision of control, as made available for example by the use of anelectronic initiation system, in addition to the use of specific blastparameters.

[0007] Enhancement (increase) of rockpile displacement in a desireddirection may be achieved by manipulating the inter-hole delay betweenblastholes, as well as the in-hole initiation within specific blastgeometries. In accordance with the present invention these delays arecontrolled with great precision by using an adjustable, highly preciseinitiation system such as an electronic initiation system. Specificblast geometries to enhance the rockpile displacement in a particulardirection include the use of an optimised blasthole pattern which ispreferably a staggered pattern such that the ratio of inter-hole spacingalong rows of blastholes (where the rows are taken to be perpendicularto the direction of required displacement) to the perpendicular distancebetween rows is in the range 1:2 to 3:2 and, preferably, in the range7:10 to 6:5. Most preferably the ratio is in the range 7:10 to 1:1. Therows are preferably drilled parallel to any pre-existing ornewly-created free faces in the blast field which are perpendicular tothe desired direction of displacement. The blasthole orientation mayalso be manipulated to enhance rockpile displacement. In this embodimentthe blastholes are generally inclined with the hole toe upwards in thesame direction as the required displacement at an acute angle to thevertical, typically in the range up to 45 degrees. The explosive massesand energies within the blastholes may also be manipulated to controlrockpile displacement. Usually, for maximum displacement the explosivemasses and energies are maximised within the constraints of localenvironmental considerations, such as the avoidance of excessivevibration or overpressure levels and hazardous rock ejections.

[0008] Within such blast geometries, the displacement in a desireddirection may be increased by the use of highly precise short inter-holedelays along rows of blastholes (where the rows are generallyperpendicular to the desired direction of displacement). Specificallythe inter-hole delays are typically from 0 to 4 ms per metre ofinter-hole spacing (where the spacing is defined as the hole separationin such rows). The precise delay interval chosen may depend upon factorssuch as rock type and condition, and blast geometry. In a preferredembodiment the inter-hole delays are from 0 to 2 ms per metre ofinter-hole spacing for most rock types. The specific inter-hole delaychosen from this range is the shortest delay possible that does notprovide excessive vibration or blast damage. Use of a highly precisedelay system, such as an electronic initiation system, allows thesedelays to be controlled to within a tolerance of less than onemillisecond.

[0009] A further aspect of the invention for regions where muckpiledisplacement is to be enhanced is to use two or more such high precisioninitiators within each blasthole with a delay of two milliseconds orless, preferably zero, between them. Preferably one of these initiatorsis located close to the bottom, or toe, of the blasthole and the othersare located further up the explosive column at regular intervals.

[0010] In addition, it has been found that rockpile displacement in thedirection perpendicular to the rows is enhanced by the use of selectedratios of time delay between rows of holes (the inter-row delay) to thedelay between holes along a row (the inter-hole or intra-row delay).Typically, this ratio will be in excess of 5:1 and, preferably, inexcess of 25:1.

[0011] The inter-hole delay time per metre of blasthole spacing isusually constant along each row, but may be varied, even between anypair of holes. The inter-row delay time per metre of rockpile burden maybe kept constant or varied from row to row according to the muckpileprofile required. The position of the primary initiator withinblastholes and the delay between in-hole initiators within blastholesmay also vary throughout the blast, according to the muckpile profilerequired.

[0012] In another embodiment of the invention, in order to provide aparticular rockpile profile suited to a mine excavation method, thedesign features mentioned above may be employed in areas of the blastwhere a flatter rockpile profile is required, or increased displacementin the desired direction. Conversely, in areas of the blast where asteeper profile is required, or decreased displacement in a selecteddirection, this is achieved by quite different manipulations of thedelay between and/or within blastholes within different specific designsof blast geometry, explosive charge and/or blast initiation location.Specific blast geometries to reduce the displacement in a particulardirection include using a blasting pattern which preferably has largerspacing and burden distances than that used in areas where increaseddisplacement is required. A similar effect may also be achieved by usingas small a blasthole as possible while maintaining adequate rockfragmentation for subsequent mechanical excavation. The blastholediameter may be reduced from that used in areas where increaseddisplacement is required. The orientation of the blastholes may alsohave an influence on the displacement observed. Thus, in areas wherereduced displacement is required the blastholes may be inclined atreduced angles to the vertical when compared with those areas in whichincreased displacement is required. The blastholes may be inclined atacute angles to the vertical as shallow as possible, including beingangled away from the blast free face, while still effecting adequaterock fragmentation for excavation. The explosive masses and energies maybe reduced to provide reduced displacement when compared with thoseareas in which increased displacement is required. The minimum explosivemass and energy must be used to effect sufficient rock fragmentation forsubsequent mechanical excavation. Within such blast geometries, thedisplacement in a particular direction may be decreased by the use ofinter-hole delays along rows of holes greater than the inter-hole delaysalong rows where increased displacement is required. Typically, forareas requiring reduced displacement the inter-hole delay will be in therange 4 to 40 ms, for example 20 to 40 ms, per metre of inter-holespacing. The preferred delay between holes in these areas is the longestdelay that does not result in problematic disruption of later firingblastholes.

[0013] In addition, displacement may be decreased further by using aratio of delays between rows of holes (the inter-row delay) to thedelays between holes along a row (the inter-hole or intra-row delay)which is lower than the corresponding ratio for areas in which increaseddisplacement is required. Typically, for decreased displacement thisratio is in the range of 5:1 or less. The blast, or region of the blastwhere reduced displacement is required, may also be initiated atlocations distant from any pre-existing free faces, hence initiating theblast, or region of the blast, from the back towards the front. Multipleblast initiation locations may thus be used, in contrast to conventionalpractice, which seldom uses more than one blast initiation location.

[0014] A particular refinement of the method of the invention,especially for use in areas where the full displacement of the rockpileis to be maximised, such as in cast blasting, without causingenvironmental problems such as excessive overpressure is to use longerinter-hole delays, preferably greater than 4 ms per metre of blastholespacing in all or part of the front (or first firing) one or two rowsand reverting to high precision shorter inter-hole delays (as specifiedabove in the range 0 to 4 ms per metre of inter-hole spacing) in thelatter part of the row or in subsequent rows.

[0015] Practical applications of the present invention includemaximising the extent of material cast (or “thrown”) to a final spoilposition whilst simultaneously minimising the amount of materialrequired to be rehandled by the excavator in producing interim platformsor surfaces from which to operate for further excavation. This enablesthe total amount of material to be handled by the excavator to beminimised, particularly in dragline operations. Such muckpile profilesmay be optimally achieved through the application of differential blastdesign throughout the blast field as described herein.

[0016] In accordance with the present invention, the overalldisplacement of the rockpile in the final direction of spoil may also beincreased to increase the overall productivity of excavation bydecreasing the distance through which material is moved by theexcavator. The invention may also be used to provide flatter, morespread out rockpiles for improving front-end loader productivity.Conversely, the invention may be used to provide steeper or tallerrockpiles for improving productivity of certain equipment such as faceshovels, or for increasing the rockpile voidage to enable easierdigging. The invention may also be used to limit rockpile displacementin ore mines to enable improved ore/waste delineation and to maximisethe concentration of ore recovered from the blast. The excavationprocess may also be enhanced by providing rockpiles in which a desiredportion of the rockpile is located to provide easy equipment accesswhile simultaneously providing an increased extent of material cast tofinal spoil in other parts of the rockpile.

[0017] Throughout this specification and the claims which follow, unlessthe context requires otherwise, the word “comprise”, and variations suchas “comprises” and “comprising”, will be understood to imply theinclusion of a stated integer or step or group of integers or steps butnot the exclusion of any other integer or step or group of integers orsteps.

The claims defining the invention are as follows:
 1. A method ofblasting in which rockpile profile of a blast field is tailored bycontrol of rockpile displacement over the blast field as a result ofblasting, this control being achieved by precise control of detonationdelay times between and/or within individual blastholes in the blastfield in combination with the control of one or more other blastparameters.
 2. A method according to claim 1, wherein the one or moreblast parameters are blasthole geometry, explosive charge and blastinitiation location.
 3. A method according to claim 1, whereindetonation delay times are controlled within a tolerance of less thanone millisecond of the required and intended delay time.
 4. A methodaccording to claim 1, wherein the detonation delay times are controlledusing an electronic initiation system.
 5. A method according to claim 4,wherein the electronic initiation system is programmable.
 6. A methodaccording to claim 1, wherein rockpile displacement in a desireddirection is controlled by manipulating the inter-hole detonation delaybetween blastholes and/or the inter-row detonation delay between rows ofblastholes.
 7. A method according to claim 1, wherein rockpiledisplacement in a particular direction is increased by use of ablasthole pattern in which the blastholes are staggered such that theratio of inter-hole spacing along rows of blastholes (where the rows aretaken to be perpendicular to the desired direction of displacement) toperpendicular distance between rows is in the range 1:2 to 3:2.
 8. Amethod according to claim 7, wherein rows of blastholes are drilledparallel to any pre-existing or newly-created free faces in the blastfield which are perpendicular to the desired direction of rockpiledisplacement.
 9. A method according to claim 1, wherein the blastholesare generally inclined with the hole toe upwards in the same directionas the desired rockpile displacement and at an acute angle to thevertical.
 10. A method according to claim 7, wherein the displacement ina desired direction is increased by the use of inter-hole detonationdelays along rows of blastholes (where the rows are generallyperpendicular to the desired direction of displacement) of from 0 to 4ms per metre of inter-hole spacing (where the spacing is defined as thehole separation in such rows).
 11. A method according to claim 5,wherein rockpile displacement is increased by use of two or moreelectronic initiators within each blasthole with a delay between eachsystem of two milliseconds or less.
 12. A method according to claim 11,wherein one of the initiators is located close to the toe of theblasthole and other initiators are located further up the blasthole atregular intervals.
 13. A method according to claim 1, wherein rockpiledisplacement in a direction perpendicular to a row of blastholes isincreased by use of selected ratios of detonation delay time betweenrows of holes (the inter-row delay) to the detonation delay time betweenholes along a row (the inter-hole delay), this ratio being in excess of5:1.
 14. A method according to claim 1, wherein rockpile displacement isdecreased by using a ratio of detonation delay time between rows ofholes (the inter-row delay) to the detonation delay time between holesalong a row (the inter-hole or intra-row delay) which is lower than thecorresponding ratio for areas in which increased displacement isrequired.
 15. A method according to claim 14, wherein the ratio is inthe range of 5:1 or less.
 16. A method according to claim 1, in whichrockpile displacement in a blast field comprising at least three rows ofblastholes is maximised without causing environmental problems by use ofinter-hole detonation delay times of greater than 4 ms per metre ofblasthole spacing in all or part of the front one or two rows and by useof inter-hole detonation delay times in the range 0 to 4 ms per metre ofinter-hole spacing in a latter part of the row or subsequent rows ofblastholes.
 17. A method according to claim 1, wherein a combination ofdetonation delay time and one or more blast parameters selected fromblast geometry, explosive charge and blast initiation location areapplied differentially over different parts of the blast field.
 18. Amethod according to claim 1, wherein rockpile displacement in aparticular direction is increased by use of a blasthole pattern in whichthe blastholes are staggered such that the ratio of inter-hole spacingalong rows of blastholes (where the rows are taken to be perpendicularto the desired direction of displacement) to perpendicular distancebetween rows is in the range 1:2 to 3:2, by use of inter-hole detonationdelays along rows of blastholes of from 0 to 4 ms per metre ofinter-hole spacing (where the spacing is defined as the hole separationin such rows), and by use of selected ratios of detonation delay timebetween rows of holes (the inter-row delay) to the detonation delay timebetween holes along a row (the inter-hole delay), this ratio being inexcess of 5:1.
 19. A method according to claim 18, wherein rockpiledisplacement in a particular direction is increased by use also of twoor more electronic initiators within each blasthole with a delay betweeneach initiator of two milliseconds or less.
 20. A method according toclaim 1, wherein rockpile displacement in a particular direction isdecreased by use of a blasthole pattern in which the blastholes arestaggered such that the ratio of inter-hole spacing along rows ofblastholes (where the rows are taken to be perpendicular to the desireddirection of displacement) to perpendicular distance between rows is inthe range 1:2 to 3:2, by use of inter-hole detonation delays along rowsof blastholes of from 4 to 40 ms per metre of inter-hole spacing (wherethe spacing is defined as the hole separation in such rows), and by useof selected ratios of detonation delay time between rows of holes (theinter-row delay) to the detonation delay time between holes along a row(the inter-hole delay), this ratio being 5:1 or less.
 21. A methodaccording to claim 1, wherein rockpile displacement is controlled byprecise control of detonation delay times between and/or withinindividual blastholes in a blast field in combination with control of atleast one blast parameter selected from blasthole diameter, blastholeorientation, explosive mass, explosive energy and inter-hole detonationdelay.
 22. A method according to claim 21, wherein the blastholediameter is reduced to produce decreased rockpile displacement.
 23. Amethod according to claim 21, wherein the blasthole is inclined at areduced angle to the vertical to produce decreased rockpiledisplacement.
 24. A method according to claim 23, wherein the blastholeis angled away from a free face in the blast field.
 25. A methodaccording to claim 21, wherein the explosive mass is reduced to producedecreased rockpile displacement.
 26. A method according to claim 21,wherein the explosive energy is reduced to produce decreased rockpiledisplacement.
 27. A method according to claim 21, wherein the rockpiledisplacement in a particular direction is decreased by use of inter-holedetonation delays along rows of blastholes greater than the inter-holedetonation delays along rows where increased displacement is required.28. A method according to claim 27, wherein the inter-hole detonationdelay is in the range 4 to 40 ms per metre of inter-hole spacing toproduce decreased rockpile displacement.
 29. A method according to claim21, wherein rockpile displacement is controlled by blast initiationlocation, reduced rockpile displacement being achieved by blastinitiation distant from any pre-existing fee faces in the blast field.30. A method according to claim 29, wherein reduced rockpiledisplacement is achieved by blast initiation from the back towards thefront of the blast field.
 31. A method according to claim 21, whereinthe blasthole diameter is increased to produce increased rockpiledisplacement.
 32. A method according to claim 21, wherein the blastholeis inclined at an increased angle to the vertical to produce increasedrockpile displacement.
 33. A method according to claim 21, wherein theexplosive mass is increased to produce increased rockpile displacement.34. A method according to claim 21, wherein the explosive energy isincreased to produce increased rockpile displacement.